Lysenko and Genetics

Lysenko's contribution printed in the summer number of SCIENCE AND SOCIETY will certainly "give occasion to the enemy to blaspheme." I have little doubt that he has gone too far in some directions, but it is important to see what there is of value in his criticism of orthodox genetics.

He begins by attacking the theory, which appears to be taught in the Soviet Union, that once a pure line is established, selection is useless. This theory is simply false, for the following reason. A pure line originally consists of individuals all of which are homozygous and genetically alike. But in course of time this ceases to be the case as a result of mutation, and also in the case of an allopolyploid such as wheat, of crossing over between chromosomes which do not normally cross over. Hence a pure line gradually breaks up into other approximately pure lines.

Some of these will be worse from an economic point of view than the original line. But some at any rate are better adapted to local conditions than their ancestors. Hence Lysenko is quite right in stressing the importance of selecting "elite strains of seed" from so-called pure lines. Any reader who supposes that I am taking this line because Lysenko is a Communist might do worse than read a paper which I published in the Journal of Genetics for 1936, entitled "The Amount of Heterozygosis to Be Expected in an Approximately Pure Line."

His next point, the breadth of the zone of isolation needed for different crops, has nothing to do with Mendelism as such. I have of course no means of judging who is right in this controversy, but I should be prepared to bet on Lysenko's being substantially correct.

Then we come to the question of the three-to-one ratio, which Lysenko says is a statistical, not a biological regularity. I confess that I am not quite clear what he means in this case, perhaps because his speech has been summarized. Where a three-to-one ratio is expected according to the laws of formal genetics, it is very rarely obtained with complete accuracy. The
deviations from it are due to two causes. First of all, we have deviations due to chance. Thus if we expect 30 hairy and ten smooth plants we are quite likely to get 33 and seven or 27 and 13. And this fact is of great biological importance. If plants or animals were always produced in exactly Mendelian ratios there would be a perpetual equilibrium in hybrid populations. These deviations, so far as they are random, are partly due to sampling, partly to linkage of the gene studied with other genes in the same chromosome affecting viability or fertility. Owing to these chance deviations, one type or another will ultimately disappear from a small population, and it will become homogeneous. Sewall Wright of Chicago has studied this effect in great detail. Second, when large numbers are grown, a deviation from the three-to-one ratio is usually found, because one type is fitter than the other. One of the largest lists of such deviations in any plant was published by de Winton and myself.[1] If there were no systematic deviations of this kind there would be no natural selection based on survival of the fittest, even if there were reproductive selection based on differences of fertility. Thus systematic deviations from the three-to-one ratio are a fact of extreme biological importance.

His next point, the importance of selection in the F1, or first hybrid generation, is correct if the hybrids are not between pure lines. As we saw, pure lines are ideals which are rarely quite realized, and agricultural varieties may be very far from pure lines.

Next we have the question of food. I think that nine times out of ten Lysenko is wrong, that is to say that you cannot improve a breed of animals by improving its food. But there are cases where this is possible, and they may be common enough to make Lysenko's principle of great practical value. The clearest of such cases was discovered at Bar Harbor, Maine, by Little's group of workers on mouse genetics and has been specially studied by Bittner. For many years they had kept different pure lines of mice. Each line had a characteristic liability to mammary cancer in females. In one line 90 per cent of all females who did not die of some other cause before the age of two years would develop this disease, in another line only 5 per cent. The members of the immune line were no more likely to develop it if they were caged for months with the susceptible line. The liability seemed to be hereditary. But it turned out that if the young of the susceptible line were separated from their mothers at birth and suckled by immune females they were much less likely to become cancerous. And this partial immunity is handed on to their children.

Nothing of the kind has been discovered for other forms of cancer.
And I believe it to be a rarer phenomenon than Lysenko supposes. But it is futile to deny its existence and to regard Lysenko's assertion of its possibility as in any way unscientific.

Now follows the question of grafting. Lysenko personally vouches for four cases where tomatoes have been altered by grafting. Tomatoes belong to the Solanaceae, which have long been known to be particularly susceptible to virus diseases. These diseases can be transmitted, among other methods, by grafting. Later research has shown that besides disease-producing viruses, it is possible to transmit viruses which have no obvious effect on the plant, but immunize it to one or more of the disease producers. Some of these viruses are known to be heavy proteins which reproduce (or are reproduced) within the plant cells. Lysenko claims to have evidence of transmissible agents which alter the shape of the fruit. It seems quite possible that the range of transmissible agents stretches from those which produce obviously pathological effects such as yellow patches on the leaves, to others which produce morphological effects like those of genes. Daniel and Dangeard in France have reported similar results in Compositae such as the Jerusalem artichoke.

On the other hand, I don't agree with Lysenko in believing that Michurin gave a white-fruited cherry red fruit by grafting it. There is a vast amount of practical experience in grafting cherries, apples, plums, loses, and other members of the Rosacene, and no recorded case of a permanent color change. Michurin's claims to have succeeded with hybridizations which otherwise failed, as a result of grafting, are on quite a different footing. They may or may not be confirmed by workers in other countries. But so little is known about the conditions for successful hybridization that they do not seem to be a priori improbable. And in view of the great value of Lysenko's technique of vernalization, which has been amply proved not, only in the Soviet Union but all over the civilized world, I should personally be surprised if his statements on results obtained by him were not largely correct.

But scientific pioneers are not infallible. Pasteur did more for the theory and practice of fermentation than any other man. Yet he made some big mistakes. Having discovered that the usual agents of fermentation, such as yeasts and bacteria, were alive, he denied the possibility of fermentation by nonliving substances. Yet today thousands of different enzymes are known, about twenty have even been crystallized by Sumner, Northrop, and others, mostly in the U.S.A. In the same way Lysenko, who is right in pointing out that the majority of characters showing Mendelian inheritance are of little economic importance, is quite wrong in
supposing that none of them are.

I take a simple example from British agricultural practice. Two dominant sex-linked genes, for barred feathers and for silver as opposed to gold feathers, show up in newly hatched chicks. Thus by a suitable cross, for example of a Light Sussex hen and a Rhode Island Red rooster, we can get chickens whose sexes can be separated at once and given different food. So long as ten years ago a single British firm was raising 800,000 chicks a year from such crosses. This was done with severely practical motives, and not to confute Lysenko. If his authority prevents similar practice in the Soviet Union he will be doing a disservice to socialism.

In the same way, I am sure that he goes much too far in his attack on the chromosome theory. His statement that "any hereditary properties can be transmitted from one breed to another even without the immediate transmission of chromosomes" is, in my opinion, absolutely false, and I think that anyone with practical experience of grafting roses or apples would agree with me. But it is equally false to say that no hereditary properties can be so transmitted. The correct statement is as above, but substituting "some" for "any."

In the same way Lysenko was wrong if he referred to the theories of current genetics, such as the three-to-one ratio and the like, as "fantasies." They are not fantasies, but approximations. Copernicus's theory that the planets went round the sun in circles was an approximation. Kepler's theory that they moved in ellipses was a better approximation. The Newton-Laplace theory was yet a better- approximation, but it was still undialectical, as it did not allow for any real history of the solar system in the sense of irreversible change. Then Kant and George Darwin showed that the solar system had undergone and would undergo slow and irreversible changes through tidal friction, with not only the moon but most of the planets moving in slowly widening orbits. Various developments of the theory of relativity suggest other slow changes.

Although the Copernican and Newtonian systems were inadequate, they were great advances on the systems of Ptolemy, Kidinnu, and other earlier astronomers. And I think posterity will rank Mendel with Copernicus or Kepler, though hardly with Newton.

It must not be supposed that Lysenko stands alone in his criticism of formal genetics and his belief that breeds can be altered by feeding. Some of his views are shared, for example, by .J. L. Hammond of Cambridge, England. I think that he has gone too far, but he may well have done a service to Soviet genetics by making his more traditionally minded colleagues examine not only the theoretical foundations of their work, but its relation to agricultural practice.

In the same number of SCIENCE AND SOCIETY Polyakov criticizes my mathematical work. Probably his criticism refers mainly to that summarized in The Causes of Evolution in 1930. He says that it includes "no consideration of real biological interrelations." This is largely true, because a mathematical treatment of even the simplest evolutionary problems is difficult. One must begin with problems as abstract as the motion of two perfectly elastic billiard balls on a frictionless table. I had to begin, just as mathematical physicists had to begin, by leaving out factors of great practical importance. Wright, Fisher, and others have greatly improved my work by making it more concrete. But I have also done so myself.

For example, fifteen years ago I calculated the equilibrium which should result when the same gene was constantly being produced by mutation and destroyed by natural selection. The idea of an equilibrium was undialectical, like Copernicus's idea of planetary motion in perfect and invariable circles. But it gave results of the right order of magnitude. Then Fisher pointed out that in this case selection of modifying genes would cause slow evolutionary changes in the apparent equilibrium. Later I dealt with "real biological interrelations" and showed that in civilized human populations the relaxation of inbreeding in recent centuries had probably caused a sharp decrease in the frequency of recessive abnormalities such as amaurotic idiocy, albinism, and some types of blindness. In fact the motor bus, by breaking up inbred village communities, was a powerful eugenic agent. Here, if I am correct, I am getting down to "real biological interrelations." If I were a Newton or a Maxwell, I might have got to this point in one step. I might even have done so had I been a Marxist fifteen years ago, in which case I should have been very suspicious of equilibriums, knowing that the conflict between two tendencies such as mutation and selection may lead to apparent equilibrium, but is very apt to cause real changes, either slow evolutionary changes or qualitative leaps. I might also have been on the lookout for biological effects of technical changes in transport and communications.

I have also had to bring my theories up to date in the light of the new facts discovered in the Soviet Union by Dubinin and his colleagues in their studies of wild populations of Drosophila. I had predicted some of them, but by no means all. The fact that I had predicted some of them shows that my mathematics had a certain validity.

Any mathematical theory inevitably leaves out a good deal of relevant facts. But it is more exact than a theory expressed in words. And I believe that my own theories, inadequate as they doubtless are, were an essential step toward exact thinking in genetics.